The present invention relates to a method for sizing papers, and more particularly to a method for sizing papers using a paper sizing agent which can be used under a condition of a wide pH-range from acidic to alkaline conditions.
In a conventional method of paper making under an acidic condition (hereinafter referred to as "acidic paper making"), there have been suitably used as sizing agents, soaps or dispersions of fortified rosins, soaps of fatty acids, hydrolyzed addition products of an olefine oligomer with succinic anhydride, and the like. However, the acidic paper making involves defects such that paper machines are corroded and the strength and durability of the obtained paper are deteriorated with the passage of time.
On the other hand, a paper making under an alkaline condition (hereinafter referred to as "alkaline paper making") has no defects in the acidic paper making. Therefore, various compounds have been studied for obtaining a sizing agent suitable for use in the alkaline paper making. However, it is impossible to exhibit a satisfactory sizing effect in practical use, when using the sizing agents used in the acidic paper making as the sizing agent used in the alkaline paper making.
Further, though typical sizing agents for the alkaline paper making such as an alkenyl succinic anhydride sizing agent and an alkyl ketene dimer sizing agent have been developed, these sizing agents have the following defects.
That is, the alkenyl succinic anhydride sizing agent is poor in workability, since it cannot be stored in the state of an aqueous dispersion due to the poor hydrolysis resistance, therefore it is necessary to emulsify or disperse the sizing agent just before it is added to the paper furnish. Also, the alkyl ketene dimer sizing agent has a disadvantage that the sizing effects immediately after the end of the paper making are poor since it takes a long time to exhibit the satisfactory sizing effect. Of course, these sizing agents cannot be used in the acidic paper making using aluminum sulfate as a fixing agent.
As aforementioned, the known sizing agents can be only used in the method of paper making under the condition of the specific range of pH, and there has not yet been proposed a sizing agent capable of applying to the methods of paper making under from acidic to alkaline conditions. Accordingly, it has been desired to be developed a sizing agent which has no defects mentioned above and can be used in the paper making under a condition of a wide range of pH.
An object of the present invention is to provide a method for sizing papers using a sizing agent which does not have the above-mentioned defects, is satisfactory in the sizing effect and the workability, and can be used in the method of paper making under a condition of a wide pH-range from acidic to alkaline conditions.
The above and other objects of the present invention will become apparent from the description hereinafter.